Hundreds of asylum seekers have marched out of a Greek transit camp — hiking for hours along muddy paths and crossing a rain-swollen river — to get around a border fence and cross into Macedonia where they were later detained, authorities say.

Key points:

Asylum seekers break through to Macedonia

Macedonian authorities to send them back

UN says people stranded at Greek border are running out of patience

A Macedonian police spokeswoman said the "several hundred" migrants and refugees who had crossed into Macedonia would be sent back to Greece.

Witnesses had put the number who crossed as high as 2,000.

About 30 journalists who followed the asylum seekers were also detained.

Earlier, Macedonian police said three asylum seekers — two men and a woman — had drowned crossing a river near the Greek border that had been swollen by heavy rain.

The asylum seekers crossed the border just days before leaders from the European Union and Turkey are due to meet again to seal an agreement intended to keep migrants in Turkey from moving to Europe through Greece.